One common way to light warehouse storage racks is with linear fluorescent lamps mounted end to end. These linear devices are a natural fit for aisle applications in terms of the uniformity of illumination along the length of the aisle and shadow reduction. The size of the fluorescent source however, can result in less than ideal light delivery efficiency and top to bottom uniformity on the racks. Instead, the shelves are typically lit brighter at the top and dimmer at the bottom.
Another way to light warehouse storage racks is with high intensity discharge (HID) light sources (e.g., high pressure sodium and metal halide). The discreet nature and high lumen output (requiring fewer total lamps) make these systems more cost effective in terms of material use, installation, and operation. Optical systems were developed to take advantage of the point source nature of these lamps to improve light delivery efficiency. The relatively small size of these lamps coupled with their high light output, however, can often result in glare. The discreet size and distant spacing from one fixture to the next can also produce strong shadows. HID products used for aisle lighting are typically the same “highbay” fixtures designed to provide uniform horizontal illumination in high-ceiling open industrial areas. These highbays typically have an axially symmetric photometric distribution which, when coupled with distant fixture spacing, leads to poor uniformity along shelves or racks.
Aisle-lighters are a subset of such highbay fixtures. These luminaires typically have reflective inserts or an oblong aperture to create a photometric distribution better suited to the linear geometry and vertical visual task of rack-and-aisle applications. Aisle-lighters can be used to provide higher illuminance on the storage racks with better uniformity than standard symmetric highbays, or similar performance on the racks with greater spacing between luminaires and a subsequently reduced luminaire count. While sometimes achieving improved photometric performance, these products are far from ideal.
A more recent trend in general highbay lighting, and thus by extension aisle lighting, is high efficacy, high lumen output, electronically-ballasted fluorescent lamps (e.g., the 54W 4′ T5HO). These lamps can provide much greater lumen maintenance than HID sources while also providing superior color and “instant on” operation. The size of fluorescent lamps makes it relatively inefficient to control their luminous output in the along dimension. As such, these fixtures are typically not louvered or lensed and thus expose their bright lamps and the reflected images of the lamps to nearly all angles of view. When mounted discretely, this lack of optical control leads to the same illuminance uniformity problem along the racks suffered by HID highbays. If mounted in something closer to an end-to-end format, their size and weight present an added burden from an installation standpoint and typically to the purchase price as well.